In medical fields, radiation emission computed tomography (ECT: Emission Computed Tomography) apparatus is used that detects an annihilation radiation pair (for example, gamma rays) emitted from radiopharmaceutical that is administered to a subject and is localized to a site of interest for obtaining sectional images of the site of interest in the subject showing radiopharmaceutical distributions. Typical ECT apparatus includes, for example, a PET (Positron Emission Tomography) device and an SPECT (Single Photon Emission Computed Tomography) device.
A PET device will be described by way of example. The PET device has a detector ring with block radiation detectors arranged in a ring shape. The detector ring is provided for surrounding a subject, and allows detection of radiation that is transmitted through the subject.
Such radiation detector arranged in the detector ring of the PET device is often equipped that allows position discrimination in a depth direction of a scintillator provided in the radiation detector for enhanced resolution. First, description will be given of a configuration of a conventional PET device. As shown in FIG. 21, a conventional PET device 50 includes a gantry 51 with an introducing hole that introduces a subject, a detector ring 53 having block radiation detectors 52 for detecting radiation being arranged inside the gantry 51 so as to surround the introducing hole, and a support member 54 provided so as to surround the detector ring 53. Each of the radiation detectors 52 has a bleeder unit 55 with a bleeder circuit in a position between the support member 54 and thereof for connecting the support member 54 and the radiation detector 52. The bleeder unit 55 is coupled to a light detector 62, mentioned later, in the radiation detector 52.
Next, description will be given of a construction of the radiation detector 52. As shown in FIG. 22, the conventional radiation detector 52 includes a scintillator 61 that converts radiation into fluorescence, and a photomultiplier tube (hereinafter referred to as a light detector) 62 that detects fluorescence. The scintillator 61 has scintillation counter crystals 63 of rectangular solid that are arranged in a three-dimensional array. The light detector 62 allows discrimination about which scintillation counter crystal 63 emits fluorescence. That is, the radiation detector 52 may discriminate an incidence position of radiation in the scintillator 61.
The PET device 50 obtains images on a site of interest of the subject through detection of annihilation radiation-pairs. Specifically, the annihilation radiation-pairs having opposite directions are emitted from radiopharmaceutical that is administered to the subject introduced into the PET device 50. Two different scintillators 61 detect the annihilation radiation-pair. Radiation detection efficiency, however, is not necessarily uniform throughout the scintillators 61. Lack of uniformity of detection efficiencies leads to reduced visibility of a radiological image.
Thus, a conventional PET device 50 uses a fan-sum method for measuring in advance lack of uniformity of radiation detection efficiencies in each scintillator 61. Then, one pair of scintillators 61 detects the annihilation radiation-pair emitted from the radiopharmaceutical administered to the subject. At this time, the lack of uniformity of radiation detection efficiencies in each scintillator 61 is cancelled with reference to the acquired lack of uniformity of detection efficiencies acquired in advance. Such configuration is described, for example, in Non-Patent Literature 1.
[Non-Patent Literature 1]
IEEE TRANSACTIONS ON NUCLEAR SCIENCE (the United States), VOL. 46, NO. 4, AUGUST 1999, Page 1062-1069